In the field of polymers, one of the areas generating a lot of interest is in the development of compound materials, more specifically of nanocomposites based on clays. There are various techniques for the preparation of nanocomposites, including the methods of casting (Ogata N, Jimenez G, Kawai H, Ogihara T; J Polym Sci Part B: Polym Phys 1997), melt mixing (Sinha Ray S, Yamada K, Okamoto M, Ueda K. Nano Lett 2002; 2:1093-6) and in situ polymerisation (Messersmith P B, Giannelis E P. Chem Mater 1993; 5:1064-6). New nanocomposites and processing techniques are also described in U.S. Pat. Nos. 5,747,560; 4,618,528; 4,528,235; 4,874,728; 6,391,449; 6,486,253; 6,376,591 and 6,156,835; WO 95/14733; WO 93/04117, and more specifically with respect to the present invention in WO2007074184A1. This PCT patent application describes a new route for manufacturing nanocomposites, which may or may not be biodegradable, with antimicrobial properties based on natural products and/or capacity for fixing or controlled release of other active or bioactive substances. These nanocomposites based on phyllosilicates and/or synthetic double layered hydroxides are intercalated with various organic modifiers. Once incorporated into thermoplastic and/or thermostable matrices, they are capable of improving barrier properties against gases and vapours. The above mentioned documents are some examples of patents and literature on polymer-clay nanocomposites prepared from modified clays. These documents describe a nanocomposite material such as an exfoliated or intercalated plate, with a tactoid structure of nanometric dimensions, which comprises intercalated clay dispersed in a polymer matrix such as an oligomer, polymer or a mixture of both.
For example, U.S. Pat. No. 4,739,007 describes the preparation of Nylon-6-clay nanocomposites from montmorillonites treated with alkyl ammonium salts by the method of melt mixing.
Protection against the action of microorganisms is a basic requirement for many current applications of plastics including preservation of the quality of packaged foods, to guarantee aseptic conditions in biomedical applications, to help reduce the growth of microorganisms on exposed and work surfaces, etc. Inventions related to the manufacture of antimicrobial systems for use in the textile, pharmaceutical and food industries have been found. More specifically, U.S. Pat. Nos. 6,841,244 and 7,232,777 describe the manufacture of silver-containing fibres with antimicrobial properties. Patents KR20030038586, U.S. Pat. No. 6,224,898 and U.S. Pat. No. 7,306,777 refer to the use of nanocomposite of metal silver and polyurethane and metal silver in dendrimeric polymers respectively, with antimicrobial properties. U.S. Pat. No. 7,306,777 and DE202005020859U describe the use of germicidal materials based on silver nanoparticles applied on packaging and packing. Patent application 200703101 comprises the manufacture of passive, (bio)active and intelligent materials and packaging with antibacterial properties by the incorporation of electrospun nanofibres containing silver nanoparticles. However, no specific design has been published to date that describes the manufacture of nanocomposites based on laminar silicates in applications for protection against the action of microorganisms.
Microorganisms, and specifically bacteria, are the main cause of diseases caused by consumption of contaminated food. They can survive the thermal treatment required for canning or even contaminate food after this treatment because of the seams or leaks from the container. In addition to the potential danger to health, proliferation of microorganisms can cause changes in foods which in turn give rise to changes in their physical, chemical and organoleptic properties. Some of the traditional preservation methods such as thermal treatments, irradiation, packaging in a modified atmosphere or by the addition of salts cannot be applied to certain types of food such as vegetables, fruits and fresh meats or ready-to-eat products. The direct application of antibacterial substances on food has limited effect because these are neutralised and diffuse rapidly towards the interior of the food. Considering the above aspects, active packaging is a viable and beneficial form of limiting and controlling bacterial growth in food as the antimicrobial agents migrate slowly from the material to the surface of the product. The migration can be as extensive as required, so that it covers the time for transport, storage and is guaranteed to consumption. In the case of antimicrobial silver nanoadditives described in the present invention, once incorporated into the packaging, they can control microbial contamination by the inactivation of the enzymatic metabolism of microorganisms.
The effect of microorganisms is also undesirable in other sectors. In the field of medicine, it is essential to remove the risks of contagion in invasive treatments, of open wounds and also in routine treatments. Examples of such treatments are coatings with antimicrobial films on catheters and stethoscopes, preparation of tissues on fibres pre-treated with silver nitrate or broad-spectrum antibiotics for treatment of wounds and burns. In the textile industry with respect to fashion or working clothing, for example, the use of fibres pre-treated with antibacterial agents limits the proliferation of microorganisms induced by sweat, humidity and elevated temperatures, reducing bad body odours and risks of contagion. The accumulation and deposition of biological material on surfaces exposed to diverse environmental conditions is known as fouling. This may occur on painted boats, objects or systems exposed to conditions of high humidity or other surfaces exposed to active, aggressive or adverse environmental conditions. In the case of boats, fuel consumption can increase by up to 50% due to hydrodynamic resistance caused by the accumulation of biological material on the hull. Antimicrobial systems can act as antifouling if applied in the form of layers on the surface of the boat, ensuring that fuel consumption is optimal and cleaning and maintenance operations are reduced in frequency. In the case of water containers and tanks, covering the interior with a film of antimicrobial compounds significantly reduces the growth of algae and the generation of bad smells, so that the quality of the water in the container is guaranteed for a longer time. Coating, or manufacturing with films of antimicrobial compounds, items such as work surfaces of laboratories (clinical, microbiological, water analysis, food), of businesses where fresh foods are handled (butchers, fishmongers, etc.), of hospital and health centre wards, to mention only a few examples, guarantees appropriate conditions of hygiene for carrying out the work and removing the risk of contamination and infections. Plastic materials with antimicrobial properties can also be used in the manufacture of cranks, handlebars, handles and armrests of public transport components, in handholds and footholds in crowded places, in the manufacture of sanitary items for mass public use, in telephone headphones and microphones and audio systems in public areas and in kitchen and food transport tools; all these applications directed at reducing the risks of propagation of infections and diseases. There is emerging interest also in manufacturing ceramic items that inhibit the proliferation of microorganisms on ceramic products, for example the proliferation of mould and mildew on surfaces covered with ceramic tiles or on the points where they join together.
In the field of ceramic materials, there are patents that describe the production of antibacterial ceramic compounds with Ag2WO4 (silver wolframate) for use on sanitary items (CN101062786); ceramic compounds with antimicrobial, fungicidal and deodorant properties containing dolomite and amphiphilic composites (JP2007169109); vitreous and ceramic materials with silver incorporated as the antimicrobial agent (US2007172661, EP1711060); antimicrobial ceramic composite of metal oxides (Ag2O, Fe2O3, MnO2, etc.) for preparing antimicrobial nanocomposites of low density polyethylene for use in the food industry (KR20010083418) and antimicrobial vitreous ceramic composites for odontological applications (US2005142077). The examples above show some of the applications of antimicrobial ceramic systems that remove or reduce the risk of propagation of infections and contamination in potentially infectious environments (sanitary items for public service use, for example), in environments where the control of microbial growth is essential for carrying out activities safely (for example, tiles for floors and walls of surgeries, clinical and toxicological laboratories, fish farming centres), in formulations for the preparation and/or repair of temporary or permanent dental replacement items (odontology), and in other potential applications.
Other active properties of great interest are those of “antioxidant” nature that function by sequestration of free radicals and therefore prevent oxidation processes even in the presence of oxygen, and the ability to sequester oxygen, which prevents oxidation by oxygen capture.